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Leaf nutrients, not specific leaf area, are consistent indicators of elevated nutrient inputs

Abstract

Leaf traits are frequently measured in ecology to provide a ‘common currency’ for predicting how anthropogenic pressures impact ecosystem function. Here, we test whether leaf traits consistently respond to experimental treatments across 27 globally distributed grassland sites across 4 continents. We find that specific leaf area (leaf area per unit mass)—a commonly measured morphological trait inferring shifts between plant growth strategies—did not respond to up to four years of soil nutrient additions. Leaf nitrogen, phosphorus and potassium concentrations increased in response to the addition of each respective soil nutrient. We found few significant changes in leaf traits when vertebrate herbivores were excluded in the short-term. Leaf nitrogen and potassium concentrations were positively correlated with species turnover, suggesting that interspecific trait variation was a significant predictor of leaf nitrogen and potassium, but not of leaf phosphorus concentration. Climatic conditions and pretreatment soil nutrient levels also accounted for significant amounts of variation in the leaf traits measured. Overall, we find that leaf morphological traits, such as specific leaf area, are not appropriate indicators of plant response to anthropogenic perturbations in grasslands.

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Data availability

The data that support the findings of this study are available in the Dryad Digital Repository with the identifier https://doi.org/10.5061/dryad.qp25093.

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Acknowledgements

This work was conducted using data from the NutNet collaborative experiment, funded at the site scale by individual researchers, and coordinated through Research Coordination Network funding from NSF to E.B. and E.S. (NSF-DEB-1042132). We thank the Minnesota Supercomputer Institute for hosting project data and the Institute on the Environment for hosting the network meetings. This manuscript is an outcome of a workshop kindly supported by sDiv, the Synthesis Centre of the German Centre for Integrative Biodiversity Research Halle-Jena-Leipzig (DFG FZT 118). M.N.B. and C.N. acknowledge funding from the Portuguese Foundation for Science and Technology through principal investigator contract IF/01171/2014 and PhD fellowship SFRH/BD/88650/2012, respectively. Figures 14 and Supplementary Fig. 5 were created by Evidently So (http://evidentlyso.com.au/). The authors thank QUT’s Central Analytical Facilities (CARF), part of the Institute of Future Environment (IFE), for use of their facilities to analyse leaf nutrient concentrations.

Author information

A.C.R., E.H., J.F., M.Sc., S.M.P. and Y.M.B. developed and framed the research question(s). E.H., H.F., J.F. and J.M. analysed the data. A.C.R., A.M.M., C.A., E.L., E.P. K.H.M. and M.Sc. contributed to the data analysis. J.F. wrote the manuscript with contributions from all other authors. A.C.R., A.E., A.M.M., A.R.K., C.A.A., C.J.S., C.N., C.R., C.S.B., E.B., E.C., E.S., J.D.B., J.F., J.L.M., J.W., J.W.M., K.J.L.P., L.B., L.S., M.C.C., M.N.B., M.Sc., M.Sm., N.E., N.H., P.A.F., P.B.A., P.D.W., P.L.P., R.M., S.M.P., W.S.H., Y.H. and Y.M.B. are site coordinators. E.S., E.B., M.Sm. and W.S.H. are Nutrient Network coordinators.

Competing interests

The authors declare no competing interests.

Correspondence to Jennifer Firn.

Supplementary information

  1. Supplementary Information

    Supplementary Figs. 1–5, Supplementary Tables 1–3, Supplementary Methods and Supplementary References

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Fig. 1: Map showing the locations of the 27 NutNet experimental sites where leaf trait information was collected using a standardized protocol.
Fig. 2: Comparison of effect estimates.
Fig. 3: Percentage of variation explained by the random effects of block nested in site nested in species plus residual variation from the Bayesian hierarchical models fit with INLA for SLA, leaf nitrogen concentration, leaf phosphorus concentration and leaf potassium concentration.
Fig. 4: Structural equation model diagram representing connections between leaf traits, experimental nutrient addition treatments, and site-level average climatic and pretreatment edaphic conditions, as well as species turnover.